Three-part series exploring Australia's Great Barrier Reef, one of the natural wonders of the world and the largest living structure on our planet. Monty Halls explores its full 2000-kilometre length, from the wild outer reefs of the Coral Sea to the tangled mangrove and steaming rainforest on the shoreline; from large mountainous islands to tiny coral cays barely above sea level; from the dark depths of the abyss beyond the reef to colourful coral gardens of the shallows.